PROJECT SUMMARY Although stress has long been linked to substance use, craving and relapse, there are no available medications that target stress-induced substance use disorder (SUD). In particular, with the rise in opioid use, there is still a crucial need for developing effective pharmacological treatments that target and integrate the complexity of this disease. The long term goal of this project is to identify the key neuroendocrine pathways that are responsible for stress-induced craving in individuals with opioid use disorder (OUD) in order to better understand how they can be effectively treated. To achieve this goal, we will utilize oxytocin, as a putative pharmacological intervention, because: 1) oxytocin's neuroanatomical-neuroendocrine pathways are shared with stress hormones; 2) oxytocin modulates dopaminergic transmission, lowers stress response and mitigates drug seeking-behaviors; and 3) an increasing number of studies suggest that the oxytocin neural circuits closely interact with the endogenous opioid system. One of the most challenging aspects in designing a human laboratory study is the inclusion of an acute stress condition that represents a comprehensive naturalistic environment for OUD individuals. Hence, testing pharmacotherapies in stress-induced opioid use models in laboratory paradigms is critical for the identification and development of therapeutic interventions to prevent drug use. Pharmacological challenges such as yohimbine, an ?-2 adrenoceptor antagonist, have been shown to activate central stress response in addition to increasing sympathetic nervous system activity, facilitating recall of traumatic memories and increasing heroin craving in opioid-dependent patients. Thus, for this proposal we will integrate oxytocin (pharmacological therapy), with a cue-reactivity paradigm (specific for opioid cues) and yohimbine (neuroendocrine stress activation) in patients receiving opioid replacement therapy (ORT) with buprenorphine/naloxone. The central hypothesis of this proposal is that stress-induced opioid craving will diminish in patients administering oxytocin in addition to ORT. We will use behavioral and neuropsychopharmacological approaches to test our central hypothesis in three Specific Aims. Aim 1: to assess the effects of oxytocin on cue-induced opioid craving after yohimbine stress-induced in patients with OUD. Aim 2: to assess whether baseline levels of stress and anxiety moderate the effects of oxytocin on cue-induced opioid craving after yohimbine-matched placebo administration in patients with OUD. Aim 3: to assess the safety and tolerability of oxytocin and yohimbine in stressed and anxious OUD patients receiving buprenorphine/naloxone. In these aims, targeted pharmacological manipulation of stress and oxytocin will be employed to examine the extent to which stress-induced craving can be reversed. The proposed research is significant because, using pharmacological probes, it will provide a much needed insight into the fundamental neurobiological mechanisms underlying stress-induced opioid craving with the goal to improve therapeutic outcomes for this population.